a chip on your shoulder
a chip on (one's) shoulder
An attitude that leads one to become combative or easily angered. Fred has such a chip on his shoulder—you never know what's going to set him off next. She won't admit it, but Kate has a chip on her shoulder when it comes to discussing her career.
a chip on your shouldera strong and usually long-standing inclination to feel resentful or aggrieved, often about a particular thing; a sense of inferiority characterized by a quickness to take offence. informal
In 1830 the Long Island Telegraph described the practice which gave rise to this expression: ‘When two churlish boys were determined to fight, a chip would be placed on the shoulder of one, and the other demanded to knock it off at his peril’.